This invention relates to a process of producing compacted, dehydrated, vegetable products of increased density by predrying, compressing, and redrying vegetables under certain conditions described hereinafter to obtain such vegetables in a form that is highly storage stable and readily rehydratable to form vegetable morsels closely resembling the vegetables prior to dehydration and compression thereof, the vegetables being quite acceptable after rehydration from the compressed and redried form.
Highly compacted, freeze-dehydrated vegetables which are dense and, therefore, occupy comparatively small space for the amount of nutrients provided thereby are well-known, particularly in the field of military rations. However, the preparation of such compacted, dehydrated vegetables has heretofore been very expensive since the production of such products has involved freeze-vacuum-dehydration. This is a high-cost method of removing moisture from foods. Furthermore, it produces very brittle materials which, if compressed in the brittle state, shatter. In the case of vegetables, the identity of morsels of the vegetables would be completely lost. Rehydration of such a product would result in a mushy product which in most cases whould have a very low acceptability rating.
Various attempts have been made to reduce the volumes and increase the densities of dehydrated vegetables without destroying their abilities to return to substantially the conditions they were in prior to dehydration. One such method has involved remoistening a freeze-dried vegetable enough to plasticize the vegetable matter and permit compression thereof without shattering morsels of the vegetable. Such a procedure requires time-consuming equilibration of moisture sprayed onto the freeze-dried vegetable before compression of the vegetable can be carried out if shattering is to be avoided. A procedure of this type is disclosed in Ishler, U.S. Pat. No. 3,385,715.
It has been proposed that freeze-vacuum-dehydration of vegetables be halted at moisture contents which would permit compression of the vegetables to the extent desired. However, this has been found to be impractical because freeze-drying involves removal of moisture by sublimation of water from the outer layers of cells leaving the core material still moist when the outer layers are very dry and brittle. It is very difficult in practice to determine when the proper average moisture content of the vegetable has been reached. Then it becomes necessary to allow the vegetable to stand in a closed vessel or area for a long time to accomplish equilibration of the moisture throughout the vegetable in order to avoid shattering the outermost portions of the vegetable during compression. A further drawback in such a procedure is that during equilibration of the moisture quality of the vegetable may deteriorate, especially in the more moist core material since the moisture migrates very slowly from the core to the surface of each vegetable morsel.
Air drying of vegetable morsels directly to a moisture content low enough for the product to be storage stable, followed by compression, has been attempted; however, this results in shattering of the structure of the vegetable morsels with the attendant production of many fines. These fines cannot be rehydrated to substantially the original physical condition of the vegetable. In addition, the fines do not adhere well when compressed.
It is generally accepted that the moisture content required in most vegetables if they are to be storage stable for at least 3 years at 70.degree. F. or at least 6 months at 100.degree. F. is no greater than 5 percent by weight. In general, the lower the moisture content, the greater the storage stability of a vegetable.
It is accordingly an object of the present invention to provide an economical method of producing compacted, dehydrated, vegetable products of increased density which possess the ability to rehydrate to substantially the physical state of the vegetable products prior to dehydration thereof.
A further object is to provide a method of producing such compacted, dehydrated vegetables of increased density which, when rehydrated, will be restored to morsel form such as the vegetable possessed prior to dehydration and compression thereof.
A still further object is to provide a method of producing such compacted, dehydrated vegetables of increased density which will have good storage stability when packaged and hermetically sealed in a container which is impervious to moisture and which will be readily rehydratable after long-term storage to restore the vegetables to morsel form such as they had prior to dehydration and compression including good acceptablilty.
Other objects and advantages will appear from the following description of the invention, and the novel features will be particularly pointed out in connection with the appended claims.